The present invention relates to Spinal Cord Stimulation (SCS) systems and more particularly to a system and method for rapidly switching between SCS system stimulation parameter sets. An SCS system treats chronic pain by providing electrical stimulation pulses through the electrodes of an electrode array, which electrode array is placed epidurally next to a patient's spinal cord. The stimulation parameter set specifies both the characteristics of the stimulation pulses provided through the electrode array, and the electrodes used to provide the stimulation pulses. An effective stimulation parameter set for a specific patient may be determined from the response of the patient to various stimulation parameters sets. However, there may be a very large number of stimulation parameter sets, and evaluating all possible sets is very time consuming, and may be impractical.
Spinal cord stimulation is a well accepted clinical method for reducing pain in certain populations of patients. An SCS system typically includes an Implantable Pulse Generator (IPG), electrodes, electrode lead, electrode lead extension, and at least one stimulation parameter set. The electrodes are implanted along the dura of the spinal cord, and the IPG generates electrical pulses which are delivered, through the electrodes, to the fibers of the spinal cord, according to the stimulation parameter set in use. Individual electrode contacts (the “electrodes”) are arranged in a desired pattern and spacing in order to create an electrode array. Individual wires within one or more electrode leads connect with each electrode in the array. The electrode leads exit the spinal column and may attach to one or more electrode lead extensions. The electrode lead extensions, or the leads, are typically tunneled around the torso of the patient to a subcutaneous pocket where the IPG is implanted.
Spinal cord stimulators and other stimulation systems are known in the art. For example, an implantable electronic stimulator is disclosed in U.S. Pat. No. 3,646,940 issued Mar. 7, 1972 for “Implantable Electronic Stimulator Electrode and Method” that provides timed sequenced electrical pulses to a plurality of electrodes. As another example, U.S. Pat. No. 3,724,467 issued Apr. 3, 1973 for “Electrode Implant For The Neuro-Stimulation of The Spinal Cord,” teaches an electrode implant for the neuro-stimulation of the spinal cord. A relatively thin and flexible strip of physiologically inert plastic is provided as a carrier on which a plurality of electrodes are formed. The electrodes are connected by leads to an RF receiver, which is also implanted.
In U.S. Pat. No. 3,822,708, issued Jul. 9, 1974 for “Electrical Spinal Cord Stimulating Device and Method for Management of Pain,” another type of electrical spinal cord stimulation device is taught. The device disclosed in the '708 patent has five aligned electrodes which are positioned longitudinally on the spinal cord. Electrical pulses applied to the electrodes block perceived intractable pain, while allowing passage of other sensations. A patient operated switch allows the patient to adjust the stimulation parameters.
Most of the electrode arrays used with known SCS systems employ between 4 and 16 electrodes. At least two electrodes are selectively programmed to act as anodes and cathodes, creating a bipolar stimulating group, or at least one electrode is selected to cooperate with the IPG case acting as a ground, creating a monopolar stimulation group. The number of stimulation groups available, combined with the ability of integrated circuits to generate a variety of complex stimulation pulses and pulse trains, presents a multiplicity of candidate stimulation parameter sets to the clinician. When an SCS system is implanted, a fitting procedure is performed to select at least one stimulation parameter set for use by the particular patient. The stimulation parameter set is selected for both treatment efficacy, and to minimize power consumption. It is desirable to try as many different stimulation parameter sets as possible during a fitting session in order to increase the likelihood of finding a near optimal set.
A known fitting method is to manually test one parameter set, and then to manually deactivate the stimulation, select a new stimulation parameter set, and then to slowly increase the stimulation level from a zero energy setting until the patient can perceive and assess the effect of the new stimulation parameter set. The testing of each stimulation parameter set is initiated at a zero energy setting. While this is a relatively safe procedure and avoids startling the patient during fitting, it is a slow procedure which prevents large numbers of combinations of parameters from being tested in a reasonable period of time. An alternative approach is to simply switch to a new stimulation parameter set at a stimulation energy setting similar to a level previously exercised. However, even if the new stimulation parameter set provides good results, switching parameter sets abruptly may provide an unpleasant sensation to the patient.
What is therefore needed is a system or method to quickly switch between stimulation parameter sets without causing uncomfortable sensations to the patient.